Features of Arthropods – jointed legged animals Section 30.1

Arthropod Diversity  All have jointed appendages – legs, antennae, and mouth parts  The largest group of animals – more arthropods than all other groups combined  Divided into two groups: those with jaws and those with fangs or pincers

Arthropod Body Plan  Jointed appendages  Segmentation  Distinct head, often with compound eyes  Exoskeleton – composed of chitin  Respiration by gills, tracheae, or book lungs  Open circulatory system  Excretion through Malpighian tubules  Many have wings

Segmentation  Individual segments exist only during larval stage  In adults the segments fuse to form three distinct regions: head, thorax, abdomen  In some the head and thorax fuse to form a cephalothorax

Three body parts – head, thorax, abdomen

Cephalothorax – combines head and thorax with a separate abdomen

Compound eyes  Each individual unit has its own lens and retina  Brain combines information to form an image  Very good for sensing movement  Some also have simple eyes which function in stabilization during flight

House fly’s compound eye

Exoskeleton  Protects internal organs & prevents drying  Flexible at the joints  Muscles are attached to the interior  Molting sheds the exoskeleton during growth

Arthropods must molt their exoskeletons as they grow

Respiration  Land arthropods use a network of tubes called tracheae which are connected to the outside by spiracles  Aquatic arthropods use gills  Some have book lungs – flattened stacks of thin tissues that absorb oxygen

Insect trachea and spiracles

Excretion  Kidney-like tubes called Malpighian tubules  These extend from the gut and are bathed with blood  Wastes enter by diffusion and leave through the anus

Malpighian tubules remove wastes